Pulse oximetry screening can identify some critical congenital heart defects (“CCHDs”), which also are known collectively in some instances as critical congenital heart disease. CCHDs are structural heart defects that often are associated with hypoxia among infants during the newborn period. Infants with CCHDs are at risk for significant morbidity or mortality. There are several defects that could be considered CCHDs. However, in the context of newborn pulse oximetry screening at the time of preparation of the present application, the Centers for Disease Control and Prevention (“CDC”) for the U.S. government classify seven (7) defects as CCHD: hypoplastic left heart syndrome, pulmonary atresia (with intact septum), tetralogy of Fallot, total anomalous pulmonary venous return, transposition of the great arteries, tricuspid atresia, and truncus arteriosus. According to the CDC, these seven CCHDs represent about seventeen to about thirty one percent (17-31%) of all congenital heart disease.
Patent ductus arteriosus (“PDA”) is common in infants with several or more of the above seven (7) defects. In the developing fetus, the ductus arteriosus (“DA”) 102 shown in FIG. 1 is the vascular connection between the pulmonary artery 106 and the aortic arch 104 that allows most of the blood from the right ventricle 110 to bypass the fetus' fluid-filled compressed lungs. During fetal development, this shunt protects the right ventricle 110 from pumping against the high resistance in the lungs 108, which can lead to right ventricular failure if the DA 102 closes in-utero.
When the newborn takes its first breath, the lungs open and pulmonary vascular resistance decreases. In normal newborns, the DA is substantially closed within twelve to twenty four (12-24) hours after birth, and is completely sealed after three (3) weeks.
In the case of PDA, high pressure oxygenated blood from the aorta 104 leaks or flows back into the pulmonary artery 112 and back to the lungs 108 with normal deoxygenated venous blood. The additional fluid returning to the lungs increases lung pressure to the point that the infant may have greater difficulty inflating the lungs. This uses more calories than normal and often interferes with feeding in infancy. Moreover, an open (patent) DA 102 alters the flow in the descending aorta 118, which, as a result, changes the blood oxygen saturation in the feet.
Without screening, some newborns with CCHDs might be missed because the signs of CCHD might not be evident before an infant is discharged from the hospital after birth. Other heart defects might be considered secondary screening targets. Some of these heart defects can be just as severe as the primary screening targets and also require intervention soon after birth. These secondary targets include aortic arch atresia or hypoplasia, interrupted aortic arch, coarctation of the aorta, double-outlet right ventricle, Ebstein anomaly, pulmonary stenosis, atrioventricular septal defect, ventricular septal defect, and single ventricle defects (other than hypoplastic left heart syndrome and tricuspid atresia).
Current CDC recommendations focus on screening infants in the well-baby nursery and in intermediate care nurseries or other units in which discharge from the hospital is common during an infant's first week of life. At the time of preparation of the present application, the CDC promulgated a CCHD screening process 200 reproduced as FIG. 2, directed toward oxygen saturation measurements, or percentages measured using, for example, a standard pulse oximeter.
According to the CDC's CCHD screening process 200 of FIG. 2, a screen is considered positive (see box 228) if (1) any oxygen saturation measurement is less than ninety percent (<90%) (in the initial screen or in repeat screens) (see boxes 206, 214, and 222); (2) the oxygen saturation measurement is less than ninety five percent (<95%) in the right hand and foot on three measures (see boxes 208, 216, and 224), each separated by one (1) hour (see boxes 204, 212, 220); or (3) a greater than three percent (>3%) absolute difference exists in oxygen saturation measurements between the right hand and foot on three measures (see boxes 208, 216, and 224), each separated by one (1) hour. Any screening that is greater than or equal to ninety five percent (≧95%) in the right hand or foot with a less than or equal to three percent (≦3%) absolute difference in oxygen saturation measurements between the right hand and foot is considered a negative screen and screening would end (see boxes 210, 218, 226, and 230).
The CDC recommends any infant receiving a positive screen receive a diagnostic echocardiogram, which would involve an echocardiogram within the hospital or birthing center, transport to another institution for the procedure, or use of telemedicine for remote evaluation. This can be expensive, disruptive, and possibly harmful to the infant. For example, at the time of preparation of the present application, an echocardiogram to verify an out-of-range (positive) screen could cost several hundred dollars.
Thus, false positives are to be avoided. The CDC believes that false positives are decreased if the infant is alert, and timing pulse oximetry screening around the time of newborn hearing screening improves efficiency.
Pulse oximetry screening may not detect all CCHDs, so it is possible for a baby with a negative screening result to still have a CCHD or other congenital heart defect.